Body imaging with sonic echo techniques is non-hazardous and cost effective. Their applications are limited by lack of sufficient resolution and contrast. In diagnosis of heart disease it is generally accepted that sonic measurements are inconclusive. Prior to heart surgery, catheterization, injection of tracer contrast elements and a multiplicity of X-rays are invariably used in preoperative diagnostics.
Existing sonic systems are two generic types: pulse and continuous wave. Inherently, the first is limited to measurements of radial range and the second to measurements of radial velocity. Dimensional resolution is inversely proportional to pulse length. Narrow pulses require high peak power. Geometric and velocity measurements are not simultaneously performed and the data is viewed separately.
Other signal waveforms and associate processes can be utilized, such as pulse Doppler, to provide measurements of distance, velocity, and pulse compression to improve geometric resolution. Distance and velocity related phase changes are cross-coupled. Either, or both, distance and velocity measurement ambiguities are introduced. The geometric resolution improvement is limited.
Sonic echo systems operate by transmitting a sonic signal into the body tissue and receiving echo signals along the transmission path from transmission impedance anomalies caused by changes in body structures. The measurement of radial distance to an anomaly is a function of the transit time between the transmission and reception of the signal. In a simple pulse system geometric resolution is inversely proportional to the pulse period; or inversely, directly proportional to the signal bandwidth. The direct proportionality is of primary importance in signal processes that increase radial distance resolution.
Radial velocity measurements are dependent upon the Doppler frequency change introduced by motion within the transmission impedance anomalies. Velocity resolution is directly proportional to the observation period.
A specific waveform and complementary signal processor capable of simultaneously detecting radial position and velocity in a non-ambiguous manner is described. Its resolving power matches theoretical capabilities; i.e., the resolution is a half wavelength of the frequency bandwidth being processed. The velocity resolution is the distance resolution divided by the signal integration time period. The finely resolved distance measurement, along with the spectral velocity information, provides the data base to image vascular anomalies, bone fractures, foreign bodies, etc.. Contrast is improved by translating velocity spectral measurements to color spectral conditioning of the image. For example, venous blood, moving towards the heart, can be colored blue and arterial blood may be colored red. Velocity gradients can be displayed by color gradation. Geometrical and velocity measurements are quantitatively defined.
The purpose of this invention is to provide means for implementing a signal processor capable of providing an improved data base for subsequent data processing as required for display.